Heat oven to 400 degrees. Grease baking pan 9 by 13 inches. In a small bowl, stir together coconut, nuts, 1/2 cup sugar and 2 tbsp. margarine. Set aside.
Mix Bisquick, 1/2 cup sugar, the remaining butter, eggs and milk. Beat vigorously 1/2 minute. Pour into pan.
Spoon chocolate over batter; with knife, cut through batter several times for marbled effect. Sprinkle cocnut over top. Bake 20-25 minutes.